This invention relates to a method for the manufacture of tetrafluoroterephthalonitrile by causing tetrachloroterephthalonitrile to react with dry powdered potassium fluoride having an excess fluorine content with reference to the chlorine content of tetrachloroterephthalonitrile in a polar solvent having a water content of not more than 0.2% by weight.
Having all the benzene rings to the exclusion of the nitrile group substituted with fluorine, tetrafluoroterephthalonitrile is useful in its unaltered form as a monomer or precussor for heat-resistant condensation polymers.
Among the methods for the manufacture of tetrafluoroterephthalonitrile, those which use fluorinated starting materials include a method which accomplishes the manufacture by amidating tetrafluoroterephthalic acid and subsequently dehydrating the resultant amide and a method which resorts to cyanation of 1,4-dibromotetrafluorobenzene (L. J. Belf et al, J. Chem. Soc., 1965, 3372).
Among the methods using nonfluorinated substances as the starting material, there is included, for example, a method which obtains tetrafluoroterephthalonitrile in a yield of 74% by allowing tetrachloroterephthalonitrile and potassium fluoride to react at 300.degree.C for 5 hours in the absence of a solvent within an autoclave [K. Ueda et al, Bull. Chem. Soc. Japan, 40, 688 (1971)]. However, since this method causes the reaction to proceed at elevated temperatures in the absence of a solvent, it entails a disadvantage in terms of corrosiveness of the reaction vessel to be used. There is another method of this kind which obtains tetrafluoroterephthalonitrile in a yield of about 44% by causing the same raw materials to react in dimethylformamide at 130.degree.to 145.degree.C for 3 hours [Fr. Pat. No. 1,397,521 (1965)]. Although this method is advantageous in that the reaction is carried out at low temperatures, it involves formation of by-products and the yield of the desired product is low. Thus, this method is not commercially feasible.
An object of the present invention is to provide a method for manufacturing tetrafluoroterephthalonitrile easily in a high yield by fluorinating tetrachloroterephthalonitrile with potassium fluoride in a solvent.